[Johnnyboy]

I sure you are aware or if you did not know the differential gears in your bus were changed by the previous owner when they first bought the coach.

Fast forward thinking, the rear end is not the same original with many proven miles. You may only have 3,000 miles on that rebuild rear end. These days I question the quality of repair work. I have had issues myself from a supposedly professional shop. 

My point. Your symptoms do sound like rear end noise, and it could be that your rear end was not setup correctly. I have also seen ride height be incorrectly set causing the drive shaft to be to many degrees out of line. 

Just some thoughts to consider in your investigation.